Biotic responses to rapid climatic changes

Qualitative and quantitative changes in fossil flora and fauna have been used in many studies to infer climatic change. Here we ask a different question: how do flora and fauna respond to climatic changes such as rapid warming or cooling? As an independent proxy for paleotemperature we take the ratio of oxygen isotopes in biogenically precipitated lake marl and in ostracod shells. This introductory paper describes the project design and the five sites on an altitudinal transect from 600 m to about 2300 m asl in the western Swiss Alps. As cases of climatic cooling and warming we use the beginning and end of the Younger Dryas as major changes, and the Gerzensee and Preboreal oscillations as minor changes. At the two sites of Gerzensee and Leysin these changes are recorded in stable-isotope ratios, and there the time scales can be derived by correlations to the GRIP ice core (Schwander et al., 2000 and von Grafenstein et al., 2000). Biotic responses to climate changes are treated in individual papers using pollen (Wick, 2000), plant macrofossils (Tobolski and Ammann, 2000), and remains of chironomids (Brooks, 2000), beetles and other insects (Lemdahl, 2000), and chydorid Cladocera (Hofmann, 2000). They are followed by a synthesis focusing on quantification of biotic responses (Ammann et al., 2000). In addition, a reconstruction of summer temperatures for the Allerød and the Younger Dryas at Gerzensee is provided by Lotter et al. (2000).

Contrasting PT paths within the Barchi-Kol UHP terrain (Kokchetav Complex): Implications for subduction and exhumation of continental crust

The Barchi-Kol terrain is a classic locality of ultrahigh-pressure (UHP) metamorphism within the Kokchetav metamorphic belt. We provide a detailed and systematic characterization of four metasedimentary samples using dominant mineral assemblages, mineral inclusions in zircon and monazite, garnet zonation with respect to major and trace elements, and Zr-in-rutile and Ti-in-zircon temperatures. A typical diamond-bearing gneiss records peak conditions of 49 ± 4 kbar and 950–1000 °C. Near isothermal decompression of this rock resulted in the breakdown of phengite associated with a pervasive recrystallization of the rock. The same terrain also contains mica schists that experienced peak conditions close to those of the diamond-bearing rocks, but they were exhumed along a cooler path where phengite remained stable. In these rocks, major and trace element zoning in garnet has been completely equilibrated. A layered gneiss was metamorphosed at UHP conditions in the coesite field, but did not reach diamond-facies conditions (peak conditions: 30 kbar and 800–900 °C). In this sample, garnet records retrograde zonation in major elements and also retains prograde zoning in trace elements. A garnet-kyanite-micaschist that reached significantly lower pressures (24 ± 2 kbar, 710 ± 20 °C) contains garnet with major and trace element zoning. The diverse garnet zoning in samples that experienced different metamorphic conditions allows to establish that diffusional equilibration of rare earth element in garnet likely occurs at ~900–950 °C. Different metamorphic conditions in the four investigated samples are also documented in zircon trace element zonation and mineral inclusions in zircon and monazite. U-Pb geochronology of metamorphic zircon and monazite domains demonstrates that prograde (528–521 Ma), peak (528–522 Ma), and peak to retrograde metamorphism (503–532 Ma) occurred over a relatively short time interval that is indistinguishable from metamorphism of other UHP rocks within the Kokchetav metamorphic belt. Therefore, the assembly of rocks with contrasting P-T trajectories must have occurred in a single subduction-exhumation cycle, providing a snapshot of the thermal structure of a subducted continental margin prior to collision. The rocks were initially buried along a low geothermal gradient. At 20–25 kbar they underwent near isobaric heating of 200 °C, which was followed by continued burial along a low geothermal gradient. Such a step-wise geotherm is in good agreement with predictions from subduction zone thermal models.

Influence of catchment quality and altitude on the water and sediment composition of 68 small lakes in Central Europe

68 lakes (63 Swiss, 2 French and 3 Italian) located in an altitudinal range between 334 and 2339m spanning a wide range of land-use have been investigated. The aim of the study was to discuss influences of geographic location, vegetation and land-use in the catchment area on the water and sediment chemistry of small lakes. Detailed quantitative description of land-use, vegetation, and climate in the watershed of all lakes was established. Surface and bottom water samples collected from each lake were analyzed for major ions and nutrients. Correlations were interpreted using linear regression analysis. Chemical parameters of water and sediment reflect the characteristics of the catchment areas. All lakes were alkaline since they were situated on calcareous bedrock. Concentrations of nitrogen and phosphorus strongly increase with increasing agricultural land-use. Na and K, however, are positively correlated with the amount of urbanization within the catchment area. These elements as well as dissolved organic carbon (DOC), Mg, Ca, and alkalinity, increase when the catchment is urbanized or used for agriculture. Total nitrogen and organic carbon in the sediments decrease distinctly if large parts of the catchment consist of bare land. No correlations between sediment composition and maximum water depth or altitude of the lakes were found.¶Striking differences in the water compositions of lakes above and below approximately 700 m of altitude were observed. Concentrations of total nitrogen and nitrate, total phosphorus, DOC, Na, K, Mg, Ca, and alkalinity are distinctly higher in most lakes below 700 m than above, and the pH of the bottom waters of these lakes is generally lower. Estimates of total nitrogen concentrations, even in remote areas, indicate that precipitation is responsible for increased background concentrations. At lower altitudes nitrogen concentrations in lakes is explained by the nitrogen loaded rain from urban areas deposited on the catchment, and with high percentages of agricultural land-use in the watershed.

Plio-Pleistocene diatom biostratigraphy from ODP Leg 177, Atlantic sector of the Southern Ocean

Seven sites were drilled during Ocean Drilling Program Leg 177 in the Atlantic sector of the Southern Ocean (SO) on a transect over the Antarctic Circumpolar Current from the Subantarctic to the Antarctic Zone. At four sites sediments were recovered with a Pliocene/Pleistocene sediment package of up to 580 m allowing the refinement of previous diatom zonation concepts. Samples were analyzed on stratigraphic distribution and abundance of diatom species. A refined diatom biozonation tied to the geomagnetic polarity record is proposed. For the middle and late Pleistocene two zonations applicable to the northern and southern area of the SO were constructed, considering different latitudinal distributions of biostratigraphic diatom marker species. The southern zonation for the Pleistocene relies on the occurrence of species of the genus Rouxia, R. leventerae and R. constricta n. sp. as well as on a revised last occurrence datum (LOD) of Actinocyclus ingens (0.38 Ma, late marine isotope stage (MIS) 11). The use of these new stratigraphic marker species refines the temporal resolution for biostratigraphic age assignment to up to 0.1 Myr. In particular the LOD of R. leventerae as an indicator for the MIS 6/5 boundary (Termination II) will improve future dating of carbonate-free Antarctic sediments. These new data were obtained from sediments of Sites 1093 and 1094 (Antarctic Zone). The northern zonation for the middle and late Pleistocene time interval is based on the Pleistocene abundance pattern of Hemidiscus karstenii which was already proposed by previous investigations (e.g. Gersonde and Barcena, 1998). One new species (R. constricta) and two new combinations (Fragilariopsis clementia, Fragilariopsis reinholdii) are proposed in this study.

Relative abundance and ranges of selected diatoms from Pliocene-Pleistocene sections of ODP Leg 177, Atlantic sector of the Southern Ocean

During Ocean Drilling Program (ODP) Leg 177, seven sites were drilled aligned on a transect across the Antarctic Circumpolar Current in the Atlantic sector of the Southern Ocean. The primary scientific objective of Leg 177 was the study of the Cenozoic paleoceanographic and paleoclimatic history of the southern high latitudes and its relationship with the Antarctic cryosphere development. Of special emphasis was the recovery of Pliocene-Pleistocene sections, allowing paleoceanographic studies at millennial or higher time resolution, and the establishment of refined biostratigraphic zonations tied to the geomagnetic polarity record and stable isotope records. At most sites, multiple holes were drilled to ensure complete recovery of the section. A description of the recovered sections and the construction of a multihole splice for the establishment of a continuous composite is presented in the Leg 177 Initial Reports volume for each of the sites (Gersonde, Hodell, Blum, et al., 1999). Here we present the relative abundance pattern and the stratigraphic ranges of diatom taxa encountered from shore-based light microscope studies completed on the Pliocene-Pleistocene sequences from six of the drilled sites (Sites 1089-1094). No shore-based diatom studies have been conducted on the Pliocene-Pleistocene sediments obtained at Site 1088, located on the northern crest of the Agulhas Ridge, because of the scattered occurrence and poor preservation of diatoms in these sections (Shipboard Scientific Party, 1999b). The data included in our report present the baseline of a diatom biostratigraphic study of Zielinski and Gersonde (2002), which (1) includes a refinement of the southern high-latitude Pliocene-Pleistocene diatom zonation, in particular for the middle and late Pleistocene, and (2) presents a biostratigraphic framework for the establishment of age models of the recovered sediment sections. Zielinski and Gersonde (2002) correlated the diatom ranges with the geomagnetic polarity record established shipboard (Sites 1090 and 1092) (Shipboard Scientific Party, 1999c, 1999d) and on shore (Sites 1089, 1091, 1093, and 1094) by Channell and Stoner (2002). The Pliocene-Pleistocene diatom zonation proposed by Zielinski and Gersonde (2002) relies on a diatom zonation from Gersonde and Bárcena (1998) for the northern belt of the Southern Ocean. Because of latitudinal differentiation of sea-surface temperature, nutrients, and salinity between Antarctic and Subantarctic/subtropical water masses, the Pliocene-Pleistocene stratigraphic marker diatoms are not uniformly distributed in the Southern Ocean (Fenner, 1991; Gersonde and Bárcena, 1998). As a consequence, Zielinski and Gersonde (2002) propose two diatom zonations for application in the Antarctic Zone south of the Polar Front (Southern Zonation, Sites 1094 and 1093) and the area encompassing the Polar Front Zone (PFZ) and the Subantarctic Zone (Northern Zonation, Sites 1089-1092). This accounts especially for the Pleistocene zonation where Hemidiscus karstenii, whose first abundant occurrence datum and last occurrence datum defines the subzonation of the northern Thalassiosira lentiginosa Zone, occurs only sporadically in the cold-water realm south of the PFZ and thus is not applicable in sections from this area. However, newly established marker species assigned to the genus Rouxia (Rouxia leventerae and Rouxia constricta) are more related to cold-water environments and allow a refinement of the Pleistocene stratigraphic zonation for the southern cold areas. A study relying on quantitative counts of both Rouxia species confirms the utility of these stratigraphic markers for the identification of sequences attributed to marine isotope Stages 6 and 8 in the southern Southern Ocean (Zielinski et al., 2002).

Chronostratigraphy on sediment core CRP-2 from the Ross Sea, Antarctica

Strontium isotope stratigraphy was used to date 16 discrete horizons within the CRP-2/2A drillhole. Reworked Quaternary (<1.7 Ma) and possible Pliocene (<2.4 Ma) sediments overlie a major sequence boundary at 25.92 meters below sea floor (mbsf). This hiatus is estimated to account for c. 16 Myr of missing section. Early Miocene to ?earliest Oligocene (c. 18.6 to >31 Ma) deposits below this boundary were cut by multiple erosion surfaces of uncertain duration. Strontium isotope ages are combined with 40Ar/39Ar dates, diatom and calcareous nannofossil datum and a palaeomagnetic polarity zonation, to produce an age model for the core.

Megabenthic communities in the waters around Svalbard during POLARSTERN cruise ARK-VIII/2 (EPOS II)

Composition and distribution of megabenthic communities around Svalbard were investigated in June/July 1991 with 20 Agassiz trawl and 5 bottom trawl hauls in depths between 100 and 2100 m. About 370 species, ranging from sponges to fish, were identified in the catches. Species numbers per station ranged from 21 to 86. Brittle stars, such as Ophiacantha bidentata, Ophiura sarsi and Ophiocten sericeum, were most important in terms of constancy and relative abundance in the catches. Other prominent faunal elements were eunephthyid alcyonarians, bivalves, shrimps, sea stars and fish (Gadidae, Zoarcidae, Cottidae). Multivariate analyses of the species and environmental data sets showed that the spatial distribution of the megabenthos was characterized by a pronounced depth zonation: abyssal, bathyal, off-shore shelf and fjordic communities were discriminated. However, a gradient in sediment properties, especially the organic carbon content, seemed to superimpose on the bathymetric pattern. Both main factors are interpreted as proxies of the average food availability, which is, hence, suggested to have the strongest influence in structuring megabenthic communities off Svalbard.

Radiolarian biostratigraphy in the central Indian Ocean

Identifiable radiolarians of stratigraphic importance were recovered at eight of the sites drilled on Leg 115. The assemblages range in age from Holocene to middle Eocene (Dictyoprora mongolfieri Zone, about 48 Ma). Faunal preservation is particularly good in two stratigraphic intervals: the Holocene through upper Miocene (0-9 Ma), and the lowermost Oligocene to middle Eocene (35-48 Ma). Fluctuating rates of silica accumulation at these drill sites during the Cenozoic reflect changing tectonic and paleoceanographic conditions. In particular, the gradual closure of the Indonesian and Tethyan seaways and the northward migration of the Indian subcontinent severely restricted zonal circulation and silica accumulation in tropical latitudes during the late Oligocene through middle Miocene. By the late Miocene the Indian subcontinent had moved sufficiently north of the equator to allow trans-Indian zonal circulation patterns to become reestablished, and biosiliceous sedimentation resumed. The composition of the radiolarian assemblages in the tropical Indian Ocean is closely comparable with that of the 'stratotype' sequences in the equatorial Pacific. However, there are some notable exceptions in Indian Ocean assemblages: (1) the scarcity of the genera Pterocanium and Spongaster in the Neogene; (2) the absence of the stratigraphically important Podocyrtis lineage, P. diamesa -> P. phyxis -> P. ampla, in the middle Eocene; and (3) the scarcity of taxa of the genus Dorcadospyris, with the exception of D. ateuchus. The succession of radiolarian events was tabulated for those stratigraphic intervals where the assemblages were well preserved. We identified 55 events in the middle Eocene to earliest Oligocene, and 31 events in the late Miocene to Holocene. The succession of events is closely comparable with that of the tropical Pacific. However, there are exceptions that appear to be real, rather than artifacts of sample preservation, mixing, and core disturbance.

Diatom biostratigraphy and datum levels of sediments from ODP Leg 167 sites

Ocean Drilling Program Leg 167 represents the first time since 1978 that the North American Pacific margin was drilled to study ocean history. More than 7500 m of Quaternary to middle Miocene (14 Ma) sediments were recovered from 13 sites, representing the most complete stratigraphic sequence on the California margin. Diatoms are found in most samples in variable abundance and in a moderately well-preserved state throughout the sequence, and they are often dominated by robust, dissolution-resistant species. The Neogene North Pacific diatom zonation of Yanagisawa and Akiba (1998, doi:10.5575/geosoc.104.395) best divides the Miocene to Quaternary sequences, and updated ages of diatom biohorizons estimated based on the geomagnetic polarity time scale of Cande and Kent (1995, doi:10.1029/94JB03098) are slightly revised to adjust the differences between the other zonations. Most of the early middle Miocene through Pleistocene diatom datum levels that have been proven to be of stratigraphic utility in the North Pacific appear to be nearly isochronous within the level of resolution constrained by sample spacing. The assemblages are characterized by species typical of middle-to-high latitudes and regions of high surface-water productivity, predominantly by Coscinodiscus marginatus, Stephanopyxis species, Proboscia barboi, and Thalassiothrix longissima. Latest Miocene through Pliocene assemblages in the region of the California Current, however, are intermediate between those of subarctic and subtropical areas. As a result, neither the existing tropical nor the subarctic (high latitude) zonal schemes were applicable for this region. An interval of pronounced diatom dissolution detected throughout the Pliocene sequence apparently correspond to a relatively warmer paleoceanographic condition resulting in a slackening of the southward flow of the California Current.

Physical oceanography in the Western Bransfield Strait and Gerlache Strait during Austral summer 1995/96

n the framework of the FRUELA project, two oceanographic surveys were conducted by R/V Hespérides in the eastern Bellingshausen Sea, western basin of the Bransfield Strait and Gerlache Strait area during December 1995 and January 1996. The main hydrographic structures of the study domain were the Southern Boundary of the ACC and the Bransfield Front. The characteristics and zonation of local water masses are discussed in terms of temperature, salinity, dissolved oxygen, nutrient and inorganic carbon concentrations. Concentration intervals for water mass labelling, on the basis of chemical parameters in addition to the common theta/S-based classification, are defined. Silicate seems to be a very good discriminator for local water masses.

Fatty acids and intact polar lipids of laminated microbial sediments from St. Peter Ording, German Wadden Sea

Hidden for the untrained eye through a thin layer of sand, laminated microbial sediments occur in supratidal beaches along the North Sea coast. The inhabiting microbial communities organize themselves in response to vertical gradients of light, oxygen or sulfur compounds. We performed a fine-scale investigation on the vertical zonation of the microbial communities using a lipid biomarker approach, and assessed the biogeochemical processes using a combination of microsensor measurements and a 13C-labeling experiment. Lipid biomarker fingerprinting showed the overarching importance of cyanobacteria and diatoms in these systems, and heterocyst glycolipids revealed the presence of diazotrophic cyanobacteria even in 9 to 20 mm depth. High abundance of ornithine lipids (OL) throughout the system may derive from sulfate reducing bacteria, while a characteristic OL profile between 5 and 8 mm may indicate presence of purple non-sulfur bacteria. The fate of 13C-labeled bicarbonate was followed by experimentally investigating the uptake into microbial lipids, revealing an overarching importance of cyanobacteria for carbon fixation. However, in deeper layers, uptake into purple sulfur bacteria was evident, and a close microbial coupling could be shown by uptake of label into lipids of sulfate reducing bacteria in the deepest layer. Microsensor measurements in sediment cores collected at a later time point revealed the same general pattern as the biomarker analysis and the labeling experiments. Oxygen and pH-microsensor profiles showed active photosynthesis in the top layer. The sulfide that diffuses from deeper down and decreases just below the layer of active oxygenic photosynthesis indicates the presence of sulfur bacteria, like anoxygenic phototrophs that use sulfide instead of water for photosynthesis.

(Table 1) Species abundance at DSDP Hole 63-467

Neogene palynofloras of southern California have been all too infrequently studied. Previous investigations of Pacific Coast sediments have been largely restricted to Pacific Northwest locales. Some important studies include those by Gray (1964), Wolfe, Hopkins, and Leopold (1966), Wolfe and Leopold (1967), Hopkins (1968), Piel (1969, 1977), Ballog, Sparks, and Waloweek (1972), and Musich (1973). The only published study of southern California materials is that of Heusser (1978) on Holocene sediments of the Santa Barbara basin. Most of these studies are concerned with the microflora from a particular formation; thus they have limited stratigraphic value and in most cases involve nonmarine to marginal marine rocks where no planktonic zonation was available. Musich's (1973) study was the first attempt at tying pollen assemblages to a planktonic zonation over an extended stratigraphic interval (Miocene to Pleistocene).Its location in the southern California Borderland and the sedimentary sections sampled make Leg 63 extremely valuable in deciphering the palynologic history of the Pacific Coast Neogene. Site 467 was chosen for our initial detailed study, because the relatively slow sedimentation rate provides an almost complete Neogene sequence of mainly terrigenous sediments and reliable planktonic age control is available.The goals of this study were to: (1) establish a reference section of Neogene palynomorph assemblages; (2) develop biostratigraphic criteria for use in correlation with other localities; (3) correlate the palynologic assemblages with the planktonic zonations; and (4) study the paleoenvironmental history in the southern California Neogene.

Temperature-dependent phenology of Plutella xylostella (Lepidoptera: Plutellidae)

Temperature-dependent population growth of diamondback moth (DBM) Plutella xylostella (L.), a prolific insect pest of crucifer vegetables, was studied under six constant temperatures in the laboratory. The objective of the study was to predict the impacts of temperature changes on the population of DBM at high-resolution scales along altitudinal gradients and under climate change scenarios. Non-linear functions were fitted on the data for modeling the development, mortality, longevity and oviposition of the pest. The best-fitted functions for each life stage were compiled for estimating the life table parameters of the species by stochastic simulations. To quantify the impacts on the pest, three indices (establishment, generation and activity) were computed using the estimates of life table parameters and temperature data obtained at local scale (current scenario 2013) and downscaled climate change data (future scenario 2055) from the AFRICLIM database. To measure and represent the impacts of temperature change along the altitude on the pest; the indices were mapped along the altitudinal gradients of Kilimanjaro and Taita Hills, in Tanzania and Kenya, respectively. Potential impact of the changes between climate scenarios 2013 and 2055 was assessed. The data files included in this database were utilized for the above analysis to develop temperature dependent phenology of Plutella xylostella to assess current and future distribution along eastern African Afromontanes.

Age determination and grain size distribution of sediment core GeoB3375-1

The palaeoclimatic conditions during the Last Glacial Maximum (LGM) of southern South America and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially. Longer palaeoclimatic records covering the Late Quaternary are rare. A particularly sensitive area to Late Quaternary climatic changes is the Norte Chico, northern Chile, because of its extreme climatic gradients. Small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments. To unveil the history of shifting climatic zones in northern Chile, we present a sedimentological study of a marine sediment core (GeoB 3375-1) from the continental slope off the Norte Chico (27.5°S). Sedimentological investigations include bulk- and silt grain-size determinations by sieving, Atterberg separation, and detailed SediGraph analyses. Additionally, clay mineralogical parameters were obtained by X-ray diffraction methods. The 14C-dated core, covering the time span from approximately 10,000 to 120,000 cal. yr B.P., consists of hemipelagic sediments. Terrigenous sedimentological parameters reveal a strong cyclicity, which is interpreted in terms of variations of sediment provenance, modifications of the terrestrial weathering regimes, and modes of sediment input to the ocean. These interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern Chile (27.5°S) through the Late Quaternary. The cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles. For the palaeoclimatic signal, this means that more humid conditions coincide with maxima of the precession index, as e.g. during the LGM. Higher seasonal precipitation for this part of Chile is most likely derived from frontal winter rain of the Southern Westerlies. Thus, the data presented here favour not only an equatorward shift of this atmospheric circulation system during the LGM, but also precession-controlled latitudinal movements throughout the Late Quaternary. Precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the Northern Hemisphere monsoonal system in the Atlantic Ocean region.